1. Field of the Invention
The present invention relates to optical discs capable being written such as DVD-R, DVD-RW and the like and particularly to an optical disc suitable for recording data signals at a high density.
2. Description of the Related Art
There have been known as optical information recording mediums such as an optical disc on which information signals may be written by irradiation of a laser beam, utilizing a dye recording layer or phase changing recording layer.
In such optical discs, for example, grooves 2a to 2c are concentrically or helically provided on a transparent circular substrate 1 of an optical disc about the center thereof, as shown in FIG. 2. Lands 3a to 3c are disposed between grooves 2a to 2c. Prepits 4a to 4c are arranged on the center line thereof with a given interval. The prepits correspond to, for example, address information signals and the like.
In this case, the prepit pairs with the adjacent groove positioned at the inner peripheral side (which is directed by an arrow in the figure) in such a manner that prepits 4a to 4c correspond to grooves 2a to 2c respectively. In addition, a recording layer, a reflecting layer, a protective layer and the like are layered in turn on the surface of the transparent substrate 1 on which the grooves are formed.
In the writing operation of the optical disc, data is written in groove 2b, while for example a light beam spot 5 is controlled to trace out the groove 2b so that address information signals and the like due to cross-talk caused by prepit 4b are read out. Similarly, in the reading-out operation of the optical disc, recorded data is read out from the groove 2b, while for example a light beam spot 5 is controlled to trace out the groove 2b so that address information signals and the like due to cross-talk caused by prepit 4b are read out.
Whereas, although the recording density may be improved by reducing the track pitch in the optical disc, the reduction of the track pitch brings a problem that cross-talk caused by prepit other adjacent tracks increases i.e., prepit signals of the adjacent tracks leak out.
For example as shown in FIG. 2, when light beam spot 5 tracks groove 2b to reproduce the recorded information signals, light beam spot 5 is irradiated onto not only prepit 4b of the outer peripheral side but also prepit 4a for the adjacent track positioned at the inner peripheral side. In this case, prepit of the adjacent track i.e., prepit 4a is positioned at the inner peripheral side of the tracking groove 2b generates cross-talk, so that the quality of reproduced signals of data record in groove 2b is reduced, and at the same time, it may be difficult to read out address information signals reproduced from prepit 4b of the outer peripheral side.
The present invention has been made in view of the problem mentioned above, and its object is to provide an optical disc capable of reducing cross-talk from adjacent tracks and improving the density of recorded data.
An optical disc according to the present invention comprises;
a substrate;
grooves concentrically or helically formed on said substrate in each of which data is recorded;
lands defined between the adjacent grooves; and
prepits formed on said lands, wherein each of said prepits is disposed to be shifted from a center line of said land toward a groove to be paired without overlapping with adjacent tracks.
According to the optical disc of the invention, any unwanted influence of cross-talk does not suffer from the adjacent prepit in the inner peripheral side, since each prepit is disposed to be shifted from the center line of the land toward a groove to be paired without overlapping adjacent tracks.